As an ink jet recording method comprises jetting fine drops of ink using some of various mechanisms to form images on a recording material, the adoption thereof makes it easy to increase a recording speed and form multicolor images, and further the method requires only inexpensive apparatus. Such being the case, the ink jet recording system has acquired a remarkable popularity in recent years. In particular, recent full-color ink jet printers have achieved great reduction in ink drop size and considerable improvement in ink properties to realize the printing of high quality, including high definition and high gradation comparable to those of silver halide photography.
More specifically, the latest main-current ink jet printers having image reproducibility comparable to that of photography (hereinafter referred to as ink jet printers of photo type) are designed so that, in a highlight section of image, each minute region hitherto reproduced by one concentrated ink drop is depicted by several dilute ink drops to reduce a grainy feeling, thereby increasing their image quality. Accordingly, the amount of ink jetted in such printers is greater than that in conventional printers, so that much higher ink absorbency than before is required for recording paper.
With respect to the ink jet recording paper, on the other hand, various arts of letting the so-called coated paper, or paper having an ink-receiving layer on a base paper, have both ink absorbency and color developability as basic factors of ink jet recording suitability have so far been developed.
For instance, as the coated paper having at least two ink-receiving layers on a substrate, the recording sheet in which the ink absorbing speed of the outermost ink-receiving layer is restricted and the second layer arranged on the inner side has a higher ink absorbing speed than the outermost layer, thereby enabling the ink to penetrate deeply into the sheet, is disclosed in Japanese Tokkai Sho 55-11829 (the term "Tokkai" as used herein means an "unexamined published patent application"), the coated paper having a coating composition coated in a double layer on the same side of a substrate is disclosed in Japanese Tokkai Sho 57-107879, and the coated paper wherein the hole distribution in an ink-receiving layer is localized in specified regions is disclosed in Japanese Tokkai Sho 58-110287.
However, those coated papers provide low image densities when they are subjected to ink jet recording, and are inferior in color developability to sensitized papers for silver halide photography. In particular, the recording on conventional ink jet recording papers with ink jet printers of photo type gives rise to running of ink due to shortage of ink absorbency in those recording papers, and further causes deterioration in traveling properties of the recording papers due to cockles and undulations generated therein after recording by the ink penetrating into their base papers in an increased quantity. In an extreme case, part of the recording paper is scraped with a printing head to leave stains on images printed.
For the purpose of heightening the ink absorbency, the thickness of an ink-receiving layer is generally increased. However, increasing the thickness of an ink-receiving layer results in lowering not only the image density but also surface strength of the ink-receiving layer. Decrease in the surface strength causes problems, e.g., such that the powdery components in the surface region tend to come off. In addition, the cost of production is raised by increasing the thickness. For the purpose of elevating the surface strength, on the other hand, increasing the proportion of an aqueous binder in the ink-receiving layer results in lowering the ink absorbency. Therefore, it is not yet achieved to develop an ink jet recording paper which raises neither ink-bleeding nor ink-overflowing problem, provides highly developed color images comparable to those in silver halide photography and ensures smooth traveling when subjected to printing operations with an ink jet printer of photo type.